This is a competitive renewal application for the Training Program in Environmental Health Sciences that is based at the Harvard School of Public Health. This is an interdisciplinary and interdepartmental program that currently supports 11 predoctoral and 3 postdoctoral trainees. Twenty five Harvard University faculty members are listed as preceptors, most of these are in the Biology in Public Health (BPH) program at the Harvard School of Public Health and are members of the Kresge Center for Occupational and Environmental Health (an interdisciplinary unit that fosters research and administers the NIEHS Center Grant ES000002); the remaining preceptors are in either the Biological and Biomedical Sciences (BBS) program in the Harvard Medical Area, or in the Molecular and Cellular Biology Program based in Cambridge. The faculty preceptors are located in the following departments: Cancer Cell Biology, Environmental Health, Nutrition, Epidemiology, Immunology and Infectious Disease, Biological Chemistry and Molecular Pharmacology, Cell Biology, Microbiology and Molecular Genetics, Pathology, and Molecular and Cellular Biology. A major strength of this program lies in the fact that its home base is at a school of public health where there is a strong emphasis on the application of knowledge gained through basic research to the protection of human health from the effects of toxic environmental agents. Another strength derives from the fact the training faculty have a broad range of skills ranging from structure/function analyses of environmentally relevant macromolecules (e.g., DNA repair and recombination proteins), to molecular epidemiological studies of human gene-environment interactions, to assessments of real-life exposures of human populations to environmental pollutants. Between these, is an array of basic biological studies on how bacteria. yeast, cultured mammalian cells, knockout and transgenic mice, and humans respond to environmental agents, with emphasis on how the agents are perceived, how signals are transduced to various parts of the cell or animal, and what the biological consequences are. We believe that this represents an exciting range of research for both predoctoral and postdoctoral training. Another major strength of the proposed Training Program lies in the superb quality of the applicants to the program departments and to the labs of individual preceptors. A rigorous training is proposed for both predoctoral and postdoctoral trainees, and it is expected that this training will position the trainees for productive careers in the Environmental Health Sciences in academia, government and industry.